Analysis of the reasons for replacing document.body with document.documentElement_javascript skills

When the page content exceeds the window size, IE6 interprets the width attributes scrollWidth, clientWidth, and offsetWidth as the actual width of the content.
The last test showed that the document.body property does not return us the expected results. For example, we used document.body.clientHeight to get the "height of the visible area of ​​the page", but what we actually returned was "the actual height of the page." content height".
Then what should we do? Could it be that after adding the document DTD type, it is no longer possible to obtain attributes such as "visible area height" and "actual content width"?

scrollTop（滚动条卷过的高）：
scrollLeft（滚动条卷过的宽）：
scrollHeight（内容实际高度）：
scrollWidth（内容实际宽度）：
clientWidth（可见区域宽）：
clientHeight（可见区域高）：
offsetWidth（加滚动条宽？）：
offsetHeight（加滚动条高？）：
screenTop：
screenBottom：
screenLeft：
sheight（分辨率高）：
swidth（分分辨率宽）：
availHeight：
availWidth：

内容高度是400PX，点击查看所有属性值